Magnetic Moment of Iron

Ferromagnetism has its quantum mechanic origin in the difference of spin-up and spin-down
electron densities. It is driven by a balance between a gain in exchange energy due to larger spin-
polarization and a loss in Coulomb repulsion and kinetic energy of the electron system.

Spin-density functional theory is able to predict magnetic moments with astounding accuracy.
The present case illustrates this capability for bulk iron.